Electrical power loss while driving?

A few times in the past 2 weeks the power from the radio turned 'off' for a second and then came back 'on'. This past Saturday we were driving, at night, home on the interstate. This time when the radio went out the whole car's power went out. There was no power to the whole car for 2 or 3 seconds. (No lights in the car, no headlights, it also felt like there was no engine power) I turned off the headlights switch to 'off' and then back to 'on' and then the power came back 'on' to the whole car. It seemed fine but I pulled over to the next Rest Area. I checked the radio fuss it was fine. I checked the battery terminals and tightened the nut on the positive terminal a little bit more. The 'Check Engine" warning light has not come on nor has it ever come on during these past 2 weeks. Does anyone have an explanation for what happened? What else should I check?